U.S. Pat. No. 4,282,006 discloses a high-solids content, low-viscosity slurry comprised of carbonaceous solid material (such as coal) and liquid which can be pumped like a liquid and burned in a manner similar to the way oil is burned. The vast deposits of coal in the United States, the fact that such a coal-liquid slurry might be substantially cheaper than an equivalent amount of oil, and the need for the United States to reduce its dependence upon foreign oil indicate that such a slurry might be very important to this nation's economy.
Ideally, a slurry containing carbonaceous material and liquid should be stable under the dynamic conditions it might encounter during pumping and shipping. In the transportation of such a slurry, (such as by barge, marine tanker, rail car, or truck tank car) various stresses might be encountered. The vibrations the slurry will be subjected to will vary in both amplitude and frequency. Thus, for example, during shipboard travel when there is relatively little clearance between the hull and the harbor or river bottom, severe shaking of the ship will be caused by pressure waves from the ship's propellers. When shipboard travel occurs on the open water, by comparison, there will be more roll, and some pitch, but the amount of high frequency vibration should be relatively small. The amount of motion a slurry is subjected to during any type of travel should vary with the extent of confinement of the slurry: full tanks would slosh very little, and partially empty tanks would slosh considerably more.
One problem encountered with many prior art coal-water slurries is that they become unmixed when they are subjected to vibration, with disastrous consequences. When such a slurry is being pumped, the solid particles settle out of the slurry to the bottom of the pipe, thereby changing the solids content and other properties of the slurry, clogging the pipe, and impeding the fluid flow of the slurry; often a hard pack of solid material is formed which is difficult or impossible to readily resuspend in the slurry.
It is probable that, to some extent, some settling will occur in coal-liquid slurries subjected to vibratory conditions. It is desirable to minimize the degree of settling. It is also desirable to provide a slurry wherein, even if settling does occur, the settled particles form a "soft pack" (as opposed to a hard pack) and can be easily resuspended in the slurry.
It is an object of this invention to provide a high-solids content slurry with low viscosity comprised of carbonaceous material and liquid which has improved dynamic stability properties, in which the amount of settling caused by vibratory conditions is minimized, and whose deposits formed after having been subjected to vibratory conditions can be relatively easily resuspended. It is another object of this invention to provide a process for preparing such a slurry. It is yet another object of this invention to provide a process for improving the stability of a carbonaceous solid-liquid slurry.